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as so much of this is going to be determined by access to the mbr suite wall & area,
lets talk about your pictures. if you'll give me a little more detail so
I know what we are looking at...it will help.
picture 1
this is the between floor area ...where?
are you taking these pics thru an attic access?

picture 2
this is un-insulated metal duct between first & second floor? serves what rooms?
picture 3

The third picture does show the duct to the master bath kick plate. This is at the end of the trunk.
this is insulated flex duct... is trunk line sheet metal and ducts flex?
or some other combination?
just trying to get a handle on how your duct system is laid out.
or is this maybe added later, earlier you had said
that ducts were enclosed in drywall with the exception of the mechanical room.
where is the mechanical room located?
I realize that you may not know, as the house isn't original to you. but
I write/think aloud sometimes.

what I'm really curious about in this picture is the batts.
depending upon which way the picture is turned..you have batts both on attic
floor and the walls of the bathroom?
it is the batts in the bathroom walls that I'm trying
to determine if you have access to. do you have access or can you make access
to these areas?

picture 4
not sure what this is at all other than an insulation batt. but just looking
at the dirty ness of this batt..there is some type of air flow through the batt.
as the air moves through insulation, the dirt/dust collects on the insulation.
dirty insulation is an indication of air leakage. doesn't matter if
the insulation is on the floor, ceiling, wall or on the duct insulation at its
take off. if it is dirty, move insulation..there is the leak. big leaks cause
larger areas of dirt, small strong leaks cause more dirt to be collected in/on/thru
insulation.

picture 5
recessed lights...the bane of my existence...LOL. hard to tell...but if they have
holes in the housing they are IC (insulation contact), if no holes they are
ICAT (insulation contact air tight). with both, insulation can be in contact
with the housing. but if IC the insulation over time will show the air leaks
through the housing. years ago, we were taught in our training that one
IC recessed can equals one sq ft of un-insulated attic. because as air moves
through the insulation it reduces the performance of the insulation.
can't remember off hand what the infiltration rate of each IC light is..
but it is enough to make it worthwhile to retrofit IC to ICAT. there
are inserts you can install from inside the house to do this.

________________________________________________
now more questions:
can you see the housing of any of the recessed lights to determine IC or ICAT?

if not, you can take the bulb out from inside the house, and read the label inside the can light.
but...read the fine print. here, Juno recessed lights are common.
but the red & white sticker inside an IC light says in big print..
ICAT..then in small print...when used with the following inserts/trims.
the true ICAT has an orange & white sticker. you have to read the fine print.
it is very misleading otherwise. this info is for Halo/Juno & may not apply to
other brands way of defining IC vs ICAT.
remember that each of these cans have a hole in the sheetrock that
is covered by the trim. so it isn't only the can itself, but the penetration
in the drywall that leaks attic air into the house.

at this time, there is no insulation between floors of first and second story?
how much of the second floor has walls shared with attic space?
what type of beams are used for second story floors?
open web trusses? solid trusses? 2x's?

sorry for the long post..just hard to tell with the pics & need the info
to determine what can be done.
I'll check with mods if we start to venture into diy area. if so you can email me
by clicking my user name and going to about me tab.
hopefully it won't be necessary...but just in case.

The cure of the part should not be attempted without the cure of the whole. ~Plato

picture 1
this is the between floor area ...where?
are you taking these pics thru an attic access? 3 car garage with the far end stall attic space uninsulated, except the wall that backs to the M Bath and the other side does back to an upstairs bedroom. Other two stalls are under two upstairs bedrooms and should be insulated. I did have about 6"thick batts (sorry don't remember r value) added over the insulation you see in the picture. There is an access to this attic through the garage ceiling. So yes I am accessing through garage and took pictures of the back wall of M Bath. You should be able to make out about a 1 ft hole that was exposed to the ceiling space between first and second floor. I took the pictures and then have since closed that off and insulated the side exposed to unconditioned attic.

picture 2
this is un-insulated metal duct between first & second floor? serves what rooms? No this is a drain pipe probably toilet Just included to provide view of what is in between the floors and may answer your question on trusses?

Picture 3
is trunk line sheet metal and ducts flex? Yes I believe this comes off the end of the sheet metal duct and turns up into the m bath vanity kick plate just on the other side of the wall. I realized after looking at this that I did tell you that I didn't have any access to the duct work. I have sealed this up pretty well but could pull open again if it ends up helping.
or some other combination?
just trying to get a handle on how your duct system is laid out.
or is this maybe added later, earlier you had said
that ducts were enclosed in drywall with the exception of the mechanical room.
where is the mechanical room located? Basement

what I'm really curious about in this picture is the batts.
depending upon which way the picture is turned..you have batts both on attic
floor and the walls of the bathroom? The batts run up the backside wall of the bathroom and a bedroom to the other side. It was typical insualtion for 2 x 4 studs and poorly installed. I have since had additional insulation batts added over what you see. Contractor did explain the dirt indicated air flow. That has helped somewhat, but bathroom floor is still pretty cold / hot.
it is the batts in the bathroom walls that I'm trying
to determine if you have access to. do you have access or can you make access
to these areas? Yes I covered over the hole that was 12" high (between floors and about 10 ft long) but otherwise I have easy access to this attic space as described earlier.

now more questions:
can you see the housing of any of the recessed lights to determine IC or ICAT?

I can't get to the topside of those lights any longer since I sealed off the space. I did pull the bulb and took pictures of the labels

at this time, there is no insulation between floors of first and second story? Correct
how much of the second floor has walls shared with attic space? M Bath and one wall of a bedroom
what type of beams are used for second story floors? I think picture will confirm but look like 2 X's.
open web trusses? solid trusses? 2x's?

I'm thinking I have this side of the wall pretty well insulated (wish I'd considered what you recommended and if you think it would be worth changing I'll consider. The right end of that hole or the right end of the master bath faces the outside. Also looking straight through there (where the pictures are taken) is another outside wall about 12 ' through there. So the master bath and room below it has two outside walls. I don't recall that either of these spots in the ceiling space were insulated on the outside walls. Is it normal to insulate the outside walls in the area between floors? I guess I'm trying to picture how they would normally do that? Do they insulate the outside area before they lay down the floor or put up the dry wall below? In picture 5 with the can lights, you can barely make out that back wall. So that wall is outside and the wall to the right (can't see in any pictures).

Sorry for the orientation of pictures. They are all on their side and need to be rotated clockwise for proper orientation

No problem on the long posts, I'm guilty of that as well. Appreciate all the input. Hope I caught all of your questions...

One shows master with windows / door on north side of 2nd story, vaulted ceiling, you can see one vent under left hand window other is under far right window. The trunk is at least 15 ft from those vents.

2nd picture shows two walls in m Bath that are outside walls. This also is the area over the previous pictures showing space between floors.

wow! thanks. nice that you answered in such detail.
so, in master bath & one of the bedrooms, from the
attic side..looking at the walls..you see insulation batts.
this I think, is the reason for the temp difference.

if you were take foam sheathing boards & cover the
wall insulation of master bathroom & bedroom..
it would stop air movement and thermal transfer
from attic into these rooms.
then to continue that air sealing from down the walls
to seal between floors...
that should equalize 5 degree temp difference.

this is why I linked the pics from pdf from southface (where they call these
areas kneewalls in attic) the solution is air seal batts in stud bays.
and in your case...between floors.

I've sent a PM to Dad (admin/mod) to see if I can step by step you
through the sealing. once I hear back, I'll post.
if I can't post the detail..I'll post that & you can email me.

sound like a plan?
in the meantime...here is some foam sheathing info to explain the three common
types.
Expanded polystyrene (EPS)
Rigid foam plastic insulation manufactured from expandable polystyrene resin containing a blowing agent that is exposed to steam and subsequently molded into the desired shape resulting in a closed cell structure.

Extruded polystyrene (XPS)
Rigid foam plastic insulation manufactured by extrusion and expansion of polystyrene monomer, the base polymer, in the presence of a blowing agent resulting in a closed cell structure.

Polyisocyanurate or polyiso (PIR)
A closed cell rigid thermosetting plastic foam board manufactured from a mixture of certain types of polyols and isocyanate (polymeric methyl diphenyl isocyanate or MDI) with a blowing agent that is reacted into a rigid board.

The cure of the part should not be attempted without the cure of the whole. ~Plato

Hey Jake 12
drop me an email. my reply may be too close
to diy to post publicly.
it is certainly detailed!
to email,click my user name,
view profile, then the tab that says about me.
email is on this page.

The cure of the part should not be attempted without the cure of the whole. ~Plato

If the furnace and ac are sized properly and have just have air flow issues, here are a couple of things to ask the contractors about. Duct sealing, turning vanes and possibly air balancing. I have had good with some or all of the listed items above. You need a lot of return air for a 5 ton system maybe even needing a second return point to the furnace. Good luck.

What would the issues be if we teed off the existing supply shown in this picture

Sorry need to rotate clockwise for proper orientation...

This feeds the master bath toe kick. Could run additional supply up knee wall and into top of wall in master bath to provide another supply in bath which is the coldest / hottest spot in master suite. Line would be 10 - 15 ft long depending on where I could locate vent. That knee wall is very accessible. there is a vanity and toilet along that wall so I'm thinking putting the vent up near ceiling? I could probably get floor access to keep the supply line shorter, but I'd have to break out at least one tile to put in vent that way. This is the same area shown in previous pictures.

What would that do to the rest of my supply system? This is already at the end of the main supply line.

I met with the contractor I'm going to use to fix the return issues in the furnace room yesterday and decided to let him start on that in the next week. This idea just hit me overnight and will bounce off the contractor but thought I'd get a head start with your team...

you are only dividing between two ducts what this one duct supplies.
if you increased the size of the duct at the plenum then you could
deliver more air to the area.
changing duct size at plenum will effect total air flow of system.

I'd put this idea pretty far down on to do list.
first fix r/a issues, then mechanical room issues.
then the walls of master suite.

have you spoken to the contractor about return air
from master suite? adding a transfer grill above
door, or jump duct from master suite to hallway
would be an easy solution.
undercut of door allows for return of one supply grill.

best of luck

The cure of the part should not be attempted without the cure of the whole. ~Plato

That supply seems weak due to it coming up under vanity and coming through a small kick plate cover that heats a few feet out. I was thinking it might get better flow if I had a full size vent in the master?

The door is undercut by 1".

No they have not brought up the return air from master. I'll present the jump duct idea. I could see how that may be possible going up through attic and then they could run down the back of a closet in other bedroom that would drop right on top of the return air. Do you think that will give good result for the work involved to install? Is a transfer grill just a hole in the wall? With the cut under the door is that providing enough return as it is?

this kick plate would be a rectangular supply grill..3.5" high &xxx long?
I'm not familiar with this type of supply.

but, if you are moving the same amount of air, determined by the size of
the duct by the plenum, does it matter
what the size the supply box & grill that distrubute the air are?
Genduct??

return air:
by return from master suite..I ment the door to the master bedroom under cut 1"
returns air from one supply grill. with 2 supplies in bedroom, one in bath..this
area isn't returning enough air to return in hallway(?).

isn't one of the returns in the hallway?

transfer grill is a bit more than a hole in the wall..but not much more!
for instance to put it over door to master suite.
on hallway side the hole would be cut and grill installed.
in bedroom side of same wall..within same stud bay another
hole is cut & grill installed.
I like to put one grill higher and the other lower
to minimize sound & light transfer.

jump duct does the same thing.
more materials..installed in attic.
2 supply grill, 2 supply box & flex duct.
one supply box to inside of master suite
the other to inside hallway.
duct connected jumps air
from one room to another, so that the air supplied by
multiple drops can return to central return.

rather than modifying ductwork, think about the air sealing
of the walls in this area that we've talked about.

Happy New Year.

The cure of the part should not be attempted without the cure of the whole. ~Plato

Yes it's 3 1/2 x 11 1/2". Here are some pictures and this is connected to that flex duct in other picture.

Sorry one is upside down...

Yes there are two returns in the hall one at top of stairs and one half way down. We do leave the master door open a lot of the time and doesn't seem to make too big a difference.

Thanks for the clarification on return ducts. Did some googling and think I better understand. I was thinking it had to be connected directly to the return, but now understand it's getting it out of master and too the return.

On my Tempstar Model T9MVX100120A1 Furnace the manual instructions on filters is pretty confusing. It basically says replace filter with what was installed. Since I wasn't the original owner, when I moved in they had green "washable" filters in place 1" or less thick. The first service tech I had out made a big deal out of that and said those are "rock catchers". He tried to talk me into a Merv 16 cabinet for hundreds of dollars.
Now that I'm having the return box just ahead of the furnace modified, I wanted to check with your team to see what the straight story is on filters for this type of furnace? I'm now using the cheap 1" throw aways and do replace monthly. We don't have allergy issues or pets so not a big concern that way. Did some searching on the forum and seem to be some positive input towards better filter cabinets, especially compared to other options (IE - UV Light, etc)??

I did contact Tempstar and their response was "the unit is shipped with 2 - 16 x 20 x 1/2" filters. You can use any filter that size in the furnace."

There's a big Caution: Box that states - Risk of reduced furnace life - Failure to follow this warning could result in increase furnace operating temperature and shorten the life of the furnace. Filters specified for the furnace are rated at a max 600 FPM Air velocity and sized for the furnaces airflow rate. Replacement filters must be of equivalent type, size and rating except as described below. Disposable low-velocity filters may be used to replace washable, high-velocity filters, providing they are sized for 300 FPM or less.

The "below" infomation goes into different rack and mount configurations. Right now i have one filter just to the left side of the furnace.